Sponsons are flat projections from the sidesof a watercraft, for protection, stability, the mounting of armaments, etc.

Sponsons are most commonly used on jetskis and other personal watercraft, because they are hydrodynamic and easy to attach. On larger craft, they are far less common than such stabilizing means as pontoons, outriggers and dual hulls, due to their inherent weakness in stabilizing large hulls.

The term "sponson" for armament mounting is sometimes used for land vehicles as well.